Add a testable example.

This commit creates and an example test file that integrates nicely with
Go's example tooling.

This allows the example output to be tested as a part of running the
normal Go tests to help ensure it doesn't get out of date with the code.

bloom/example_test.go

@@ -0,0 +1,44 @@
+// Copyright (c) 2014 Conformal Systems LLC.
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package bloom_test
+
+import (
+	"fmt"
+	"math/rand"
+	"time"
+
+	"github.com/conformal/btcutil/bloom"
+	"github.com/conformal/btcwire"
+)
+
+// This example creates a new bloom filter, adds a transaction hash to it, and
+// shows how to check if the filter matches the transaction.
+func ExampleNewFilter() {
+	rand.Seed(time.Now().UnixNano())
+	tweak := rand.Uint32()
+
+	// Create a new bloom filter intended to hold 10 elements with a 0.01%
+	// false positive rate and does not include any automatic update
+	// functionality when transactions are matched.
+	filter := bloom.NewFilter(10, tweak, 0.0001, btcwire.BloomUpdateNone)
+
+	// Create a transaction hash and add it to the filter.  This particular
+	// trasaction is the first transaction in block 310,000 of the main
+	// bitcoin block chain.
+	txHashStr := "fd611c56ca0d378cdcd16244b45c2ba9588da3adac367c4ef43e808b280b8a45"
+	txHash, err := btcwire.NewShaHashFromStr(txHashStr)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	filter.AddShaHash(txHash)
+
+	// Show that the filter matches.
+	matches := filter.Matches(txHash.Bytes())
+	fmt.Println("Filter Matches?:", matches)
+
+	// Output:
+	// Filter Matches?: true
+}